Electronic signaling

There is a wide variety of methods for sending an electronic distress message. Not every method is appropriate in all situations, however. A review of signaling methods illustrates the pros and cons of each system.

The following methods are used for long-range emergency signaling. They will alert search and rescue forces to an emergency situation and provide you with a method for communicating your position.

406 EPIRBS: Probably the best overall method for hitting the panic button, with a 406 MHz emergency position-indicating radiobeacon (EPIRB) you are virtually assured of getting a distress message out. A satellite-aided system, the broadcast from a 406 EPIRB is picked up by transponders on American and Russian polar-orbiting weather satellites. The great thing about 406 transponders is that they’re "smart." After receiving a distress message, the transponder’s computer notes the satellite’s position in orbit and checks its database to determine if any satellite Earth stations are in view. If an Earth station is available, the 406 transponder rebroadcasts your recorded signal.

However, if there is no Earth station in line of sight with the 500-mile-high satellite, the 406 computer stores your distress message in memory. It waits until a station is in sight, and then rebroadcasts the distress message. Using the Doppler Shift of the message, search-and-rescue (SAR) authorities are able to put a 406 MHz EPIRB in an area of roughly 12 square nautical miles.

Better yet, 406 units include a unique ID number in their distress message. If the EPIRB’s owner has done his or her job and sent in the registration card, then SAR authorities will know not only the EPIRB’s position, but the identity of the owner and information about the boat as well.

As a second-generation EPIRB product, the 406 has tighter specifications for its transmitter and battery, making it more reliable, powerful, and effective than the first-generation units (see 121.5/243 below).

GPIRBS: What about building a GPS receiver into a 406 EPIRB? It could broadcast its GPS-derived position and greatly reduce the search area. That’s the idea behind the GPIRB. This type of distress beacon has all the advantages of a 406 EPIRB, plus the position accuracy of its onboard GPS receiver.

Because this type of distress beacon doesn’t rely on the Doppler Shift method of positioning, its signals can be picked up and relayed by geosynchronous satellites as well as polar orbiters.

121.5/243 EPIRBS: First-generation EPIRB units are still available for sale, but their drawbacks make them less desirable for the offshore sailor than a 406 EPIRB. Unlike the 406 system, the 121.5/243 setup wasn’t equipped with smart transponders. The 121.5/243 transponders have no "store and forward" capability. When the satellite transponder receives a 121.5/243 EPIRB signal, it is immediately retransmitted, regardless of whether an Earth station is view. Since Earth station coverage is by no means worldwide, there are large ocean areas where a 121.5/243 EPIRB is useless.

Also, the equipment specifications for 406 units were not as tightly written as for 406 units. Thus, 121.5/243 beacons are not as reliable or as easy for SAR forces to locate using the Doppler Shift method.

If you do have a 121.5/243 EPIRB, the improved 406 transponders on current satellites will still respond to the 121.5 frequency. They won’t store and forward it, however.

Inmarsat C: While EPIRBs can only be used for sending distress messages, Inmarsat C is primarily a communications tool that also has excellent distress signaling capabilities.

A satellite-based text-messaging system, Inmarsat C uses geosynchronous satellites as relays so mariners can send and receive text messages (including Internet e-mail) from anywhere on Earth, except for the area around the poles.Inmarsat C users have several ways they can send a distress message. If a boat is sinking and time is short, many Inmarsat C units have a red emergency button. Hold it down for five seconds and the Inmarsat C unit will send an automatic emergency message to Inmarsat headquarters in London. The message contains the vessel’s name and position. (Most current Inmarsat C transceivers have built-in GPS receivers. If not, they can accept GPS positions via the NMEA 0183 interface.) Inmarsat’s HQ in London then looks at the location of the vessel and forwards the distress message to the nearest rescue coordination center (RCC). The RCC then responds to the emergency.

If there is more time, the user can bring up a table of possible distress conditions (fire, flooding, whale impact, medical emergency, etc.) and send a generic distress message to Inmarsat HQ. A third option is write an extensively detailed distress message and send that. No matter which method is used, Inmarsat C is a reliable way to get a distress message out.Inmarsat M and Mini-M: Built primarily as satellite voice systems, neither Inmarsat M (worldwide coverage) nor Mini-M (some worldwide coverage gaps) has the safety-at-sea features inherent in Inmarsat C. If you wish to send a distress message with these systems, you must pick up the phone and call the nearest Coast Guard station.Wavetalk: A satellite phone system similar to Inmarsat Mini-M, Wavetalk provides coverage of North America and adjacent waters. Once again, if you have an emergency you have to dial a phone number (watch out for voice mail!).

HF SSB: The original long-range distress signaling method, high frequency (HF) single sideband (SSB) radio is still a good method for sending a distress call.

For decades, the standard HF distress frequency has been 2,182 kHz. And that is still true. However, the Coast Guard has stated that, as of February 1999, some of its communications stations may stop guarding 2,182. Most large commercial vessels have already abandoned 2,182 for satellite systems. Thus, a distress call on 2,182 may not be the best choice in a time-critical emergency situation.

Possibly a better strategy is to call a high-seas marine operator at one of the major coast stations like WLO, WOM, or KMI. The marine operators at these stations actively listen to their assigned calling channels and have the experience and equipment to hear and respond to even weak signals. They will quickly patch your call through to the Coast Guard.

Another option is to call on one of the four channels used by the Coast Guard for gathering position reports from commercial vessels participating in the Automated Mutual-assistance Vessel Rescue (AMVER) search-and-rescue system. Coast Guard radio operators will be able to take your emergency information and alert the nearest rescue coordination center.Short range

Once SAR forces are on the way, what are your options for signaling them once they get close? How about a homing beacon that allows a C-130 Hercules or a HH-65 Dolphin helicopter to follow the beam right to you? Actually, 121.5/243 and 406 MHz EPIRBs do broadcast a homing signal. Both types of EPIRBs use the 121.5 MHz frequency as a homing signal (so, while the new generation of EPIRBs is called 406, they actually broadcast both 406 and 121.5 MHz signals).

Another device to aid SAR personnel in locating you is something called a search and rescue radar transponder (SART). This unit will rebroadcast any radar signals it receives. This device will make you show up as a large return on a searcher’s radar screen, making it easier to find your small life raft in the big ocean.

And, of course, if you want to talk to the people trying to save you, it’s a good idea to have a handheld VHF with you in the life raft.

By Ocean Navigator